Conventionally, in a gas supply apparatus for a semiconductor control device, a pressure type flow control system FCS using an orifice has been widely used. This pressure type flow control system FCS is, as shown in FIG. 16, composed of a control valve CV, a temperature detector T, a pressure detector P, an orifice OL, an arithmetic and control unit CD, and the like, and the arithmetic and control unit CD is composed of a temperature correction/flow rate arithmetic circuit CDa, a comparison circuit CDb, an input-output circuit CDc, an output circuit CDd, and the like.
Detection values from the pressure detector P and the temperature detector T are converted into digital signals, to be input to the temperature correction/flow rate arithmetic circuit CDa, and a temperature correction and a flow rate computation are carried out therein, and a computed flow rate value Qt is input to the comparison circuit CDb. Furthermore, an input signal Qs as a set flow rate is input from a terminal In, to be converted into a digital value in the input-output circuit CDc, and the digital value is thereafter input to the comparison circuit CDb, to be compared with the computed flow rate value Qt from the temperature correction/flow rate arithmetic circuit CDa. Then, in the case where the set flow rate input signal Qs is higher than the computed flow rate value Qt, a control signal Pd is output to a drive unit of the control valve CV, and the control valve CV is driven in the opening direction. In fact, the control valve CV is driven in the valve-opening direction until a difference (Qs-Qt) between the set flow rate input signal Qs and the computed flow rate value Qt becomes zero.
The pressure type flow control system FCS itself is publicly known as described above. Moreover, the pressure type flow control system FCS is excellently characterized, in the case where the relationship that P1/P2 is greater than or equal to about 2 (i.e., so-called critical expansion conditions) is maintained between the downstream side pressure P2 of the orifice OL (i.e., the pressure P2 on the side of the process chamber) and the upstream side pressure P1 of the orifice OL (i.e., the pressure P1 on the outlet side of the control valve CV), by the flow rate Q of the gas Go flowing through the orifice OL, which becomes Q=KP1 (however K is a constant). Thus, it is possible to highly accurately control the flow rate Q by controlling the pressure P1, and the controlled flow rate value hardly changes even when the pressure of the gas Go on the upstream side of the control valve CV is greatly changed.
However, because the conventional pressure type flow control system FCS uses an orifice OL with a minute hole diameter, there may be a risk that the hole diameter of the orifice OL varies over time. As a result, there is a problem that a difference is caused between a controlled flow rate value determined by the pressure type flow control system FCS and a real flow rate of the gas Go actually flowing through the pressure type flow control system FCS. Consequently, it is necessary to frequently carry out so-called “flow monitoring” in order to detect this difference, which may highly influence the operating characteristics of semiconductor manufacturing equipment and the quality of manufactured semiconductors.
Therefore, conventionally, a flow control system that is capable of simply monitoring whether or not flow control is appropriately performed in real time has been developed in the fields of thermal type mass flow control systems and pressure type flow control systems. For example, FIG. 17 and FIG. 18 show one example thereof, and this mass flow control system (mass flow controller) 20 is composed of a flow passage 23, a first pressure sensor 27a for pressure on the upstream side, an opening/closing control valve 24, a thermal type mass flow sensor 25 that is installed on the downstream side of the opening/closing control valve 24, a second pressure sensor 27b that is installed on the downstream side of the thermal type mass flow sensor 25, a throttle unit (sonic nozzle) 26 that is installed on the downstream side of the second pressure sensor 27b, an arithmetic and control unit 28a, an input-output circuit 28b, and the like.
The thermal type mass flow sensor 25 has a rectifier body 25a that is inserted into the flow passage 23, a branched flow passage 25b that is branched from the flow passage 23 so as to have only a flow rate of F/A, and a sensor main body 25c that is installed on the branched flow passage 25b, and outputs a flow rate signal Sf denoting a total flow rate F. Furthermore, the throttle unit 26 is a sonic nozzle that flows a fluid at a flow rate corresponding to the pressure on the primary side when a pressure difference between those on the primary side and the secondary side is higher than or equal to a predetermined value. In addition, in FIG. 17 and FIG. 18, reference symbols Spa and Spb are pressure signals, reference symbols Pa and Pb are pressure, reference symbol F is a flow rate, reference symbol Sf is a flow rate signal, and reference symbol Cp is a valve opening degree control signal.
The arithmetic and control unit 28a employs the pressure signals Spa and Spb from the pressure sensors 27a and 27b, respectively, and the flow control signal Sf from the flow sensor 25, to output the valve opening degree control signal Cp as a feedback, thereby performing feedback control of the opening/closing valve 24. In other words, the flow rate setting signal Fs is input to the arithmetic and control unit 28a via the input-output circuit 28b, and the flow rate F of the fluid flowing in the mass flow control system 20 is regulated so as to correspond to the flow rate setting signal Fs. In detail, the arithmetic and control unit 28a provides feed back to the opening/closing control valve 24 by use of an output Cp (which is based on the pressure signal Spb from the second pressure sensor 27b), to control the opening or closing of the opening/closing control valve 24, thereby controlling the flow rate F of the fluid flowing in the sonic nozzle 26. Furthermore, the arithmetic and control unit 28a makes use of measurement of the actual flowing flow rate F by use of an output (i.e., the flow rate signal Sf) from the thermal type flow sensor 25, in order to check the operation of the mass flow control system 20.
Thus, in the mass flow control system 20 of the apparatus model shown in FIG. 17 and FIG. 18, because two types of measurement methods of pressure type flow measurement, using the second pressure sensor 27b for performing flow control and a flow measurement using the thermal type flow sensor 25 for monitoring a flow rate, are incorporated in the arithmetic and control unit 28a, it is possible to easily and reliably monitor whether or not a fluid at a controlled flow rate (i.e., a set flow rate FS) is actually flowing. That is, it is possible to easily and reliably monitor whether or not there is a difference between the controlled flow rate (the goal flow rate) and the real flow rate (the actual flow rate), which exerts a high practical effect.
However, there remain many problems to be solved in the mass flow control system 20 shown in FIG. 17 and FIG. 18. As a first problem to address, the arithmetic and control unit 28a is configured to control the opening and closing of the opening/closing control valve 24 by use of both signals of the output Spb from the second pressure sensor 27b and the flow rate output Sf from the thermal type flow sensor 25, and to correct the flow rate output Sf from the thermal type flow sensor 25 by use of the output Spa from the first pressure sensor 27a. In other words, the arithmetic and control unit 28a controls the opening and closing of the opening/closing control valve 24 by use of these three signals, namely, two pressure signals from the first pressure sensor 27a and the second pressure sensor 27b, respectively, and a flow rate signal from the thermal type flow sensor 25. Therefore, there is a problem that not only is the configuration of the arithmetic and control unit 28a complicated, but also stable flow control characteristics and excellently high response characteristics of the pressure type flow control system FCS are reduced by opposite factors.
As a second problem to address, there is a problem in that the installation position of the thermal type flow sensor 25, with respect to the opening/closing control valve 24, is changed. That is, in the mass flow control system 20 shown in FIG. 17 and FIG. 18, the response characteristics of the thermal type flow sensor 25 at the time of opening and closing of the opening/closing control valve 24, and the gas replacement characteristics and the vacuuming characteristics in the device main body, are greatly changed. Consequently, it is difficult to downsize the mass flow control system 20.
Furthermore, so-called “flow control” systems have been widely used for gas supply devices, and the like, in semiconductor manufacturing facilities as shown in, for example, FIG. 31. As shown in FIG. 31, a purge gas supply system Y and a process gas supply system X are connected in parallel on the upstream side of a flow control system D, and a process gas using system C is connected on the downstream side of the flow control system D. Moreover, valves V1, V2, and V3 are respectively installed along the way of the respective gas supply systems X and Y and the gas using system C.
In addition, in the fluid supply system as shown in FIG. 31, generally, the operating statuses of the valves V1 to V3 are periodically inspected, and this inspection work is absolutely imperative in order to stably supply a required process gas through the process gas using system C. Therefore, in the above-described inspections (hereinafter called checks) for the valves V1 to V3, usually, checks for the operating states of the respective valves (including the operation of a valve actuator) and checks for seat leakages of the respective valves, are carried out.
However, at the time of checks for the seat leakages of the valve V3 of the process gas using system C, and for the valves V1 and V2 on the upstream side of the flow control system D, it is necessary to detach the respective valves V1, V2 and V3 from the pipe passages, so that each valve can be checked by use of a separately provided test device. However, this takes a lot of time and effort to perform these seat leakage checks for the respective valves.
The problems relating to these inspections for the respective valves are the same as those in the pressure type flow control system with flow monitoring. That is, every time an anomaly in monitoring flow rate is detected by a flow rate self-diagnostic mechanism, it is necessary to detach the pressure type flow control system with flow monitoring from the pipe passage to inspect it, which is a problem because it takes a lot of time and effort.